This invention relates to tamper-proof valves and, more particularly, to valves having a rotatable valve member or a rotatable operator, such as butterfly valves, ball valves and plug cocks, including a locking mechanism for permitting the valve to be opened or closed, but preventing the valve member from being returned to its former position.
Quarter-turn valves may be used in applications where it is desirable for them to be designed so that, in the event the valve is improperly closed or opened, it cannot be re-opened or re-closed without special tools or must be replaced. For instance, gas supply lines to households and business establishments commonly include a shut-off valve upstream of the supply meter. An unscrupulous user wishing to by-pass the supply meter would have to close that valve to make the necessary modifications. If a shut-off valve of the above design were provided by the gas supply company, a user closing the valve would have to contact that company, either to open the valve with a special tool or to replace it, before gas service could start again.